Figure 13.

(a) Crystal structure of layered WS₂; the purple balls correspond to W atoms and the yellow balls to S atoms. (b) Optical microscope image of a six-terminal Hall bar fabricated on a crystalline WS₂ thin flake (the scale bar is 10 μm long). (c) Molecular structure of the ionic liquid employed as an electrolyte–gate dielectric. Both cation [P14]⁺ and anion [FAP]⁻ are shown. (d) Cross-section of a WS₂ ionic liquid-gated FET. A large area of gold mesh and an oxidized Ag/AgO wire are used as a gate electrode and quasi-reference electrode, respectively. When the gate electrode is biased, two electrical double layers are formed at the gate/electrolyte and semiconductor/electrolyte interfaces, enabling charge accumulation at the semiconductor surface. Reprinted with permission from ref. [85]. 2012 American Chemistry Society.